Recent evidence suggests that the Alzheimer's related protein A-beta asserts its deleterious effects through an interaction with the neurotrophin receptor p75. To understand this interaction, the proposed research aims to characterize the complex between p75 and Amyloid-beta (A-beta). Using a fibrillogenesis inhibition assay, I will first determine the minimal regions of these proteins required for a productive interaction. I will then use a combination of biochemical techniques to determine the stoichiometry of the interaction, its energetics, and the oligomerization state of the individual components within the complex. I will use these fragments for x-ray crystallography, providing an atomic resolution picture of the complex. This information will guide mutations that are predicted to disrupt the interaction. These mutations will be analyzed with biochemical experiments that quantify the effect on complex formation. If a crystal structure is unrealizable, I will use an alanine-scanning mutagenesis approach to achieve a residue level understanding of the complex. This research will provide a detailed understanding of the p75*A-beta complex that will complement existing biological data, shedding light on the mechanism of A-beta induced toxicity in Alzheimer's disease. Additionally, the assays developed through the proposed research may be useful in the screening for small molecule inhibitors of the complex. Such inhibitors would have potential as reagents for research in vivo and may also pave the way for the development of novel therapeutic compounds. PUBLIC HEALTH RELEVANCE Recent evidence suggests that the causative agent of Alzheimer's disease acts by triggering a key component of a naturally existing neural cell death pathway in the in brains of Alzheimer patients. Fundamental aspects of this triggering event will be studied using an experimental approach. The hope is to better understand this debilitating disease and pave the way for the development of new therapeutics for the treatment of Alzheimer's disease. [unreadable] [unreadable] [unreadable]